The rotors of motors with permanent magnets of known type, used especially in brushless motors, usually consist of a laminated core, that is to say, a core made up of a pack of thin metal laminations and having a principal axis that coincides with the axis of rotation of the motor.
The rotor normally has a plurality of longitudinal slots and a central hole, which extend parallel to the main axis, for accommodating the magnets and a drive shaft, respectively.
The slots form in the laminated core a sort of segment structure, forming the poles of the rotor, where each segment, which remains connected to a central portion of the laminated core surrounding the hole of the shaft, separates two adjacent slots.
The magnets extend along the axis of the rotor, in which they are positioned radially, arranged, in general, against a par of respective contact elements at the outer end of the relative slot which is generally open on the outer surface of the rotor (except for the aforesaid contact elements).
A common problem with this type of rotor linked to the method of fixing the magnets in the relative slots.
The magnets must be attached in the slots in a precise position both for the correct electromagnetic operation of the motor and so as not to trigger vibrations during operation of the motor.
In the reference rotors for this invention, that is, with the magnets positioned radially, one prior art solution glues the magnets in the relative seats. The magnets with glue on them are inserted in the relative slot and held by a special tool abutted against the outer contact elements until the glue sets.
In a different embodiment, the magnets are held in position in the slot by a tool whilst the rotor is inserted in a mould where plastic is injected. In this way, the magnets are co-pressed with the laminations and held in position by the plastic.
The aforesaid prior art solutions are relatively expensive due to the assembly complexity.
In another embodiment, which is the one most commonly used, each magnet is held abutted against the contact elements by a radially pushing spring interposed between the magnet and the central portion of the laminated core.
These springs may be single (one for each magnet) or grouped together in a singular annular element.
In this solution a major disadvantage is that given a magnet, the corresponding spring, due to the mechanical tolerances for inserting the magnet, may push the magnet in a not perfectly radial direction so that it abuts against only one of the contact elements prepared, that is, against only one of the segments which delimit the slot.
In some cases, there may be segments which are not stabilised by the magnets and which therefore vibrate during operation of the motor.
Moreover, the magnet may chip at the contact element due to the reduced contact surface of the latter.